<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        
        .box{
            /* 弹性盒子在侧轴方向没有尺寸才能拉伸 */
            /* align-items: stretch; */

            /* align-items: center; */
            /* align-items: start; */
            /* align-items: end; */



            display: flex;
            /* justify-content: space-between; */
            /* flex-start 左贴 */
            /* flex-end 右贴 */
            /* center 居中 */
            /* space-between 两端对齐 剩余均分 */
            /* space-around 两端空余 均分剩余 且盒子之间间距是两端间距的2倍 */
            /* space-evenly 各个间距都相等 */
            
            height: 300px;
            border: 1px solid red;
        }
        .box div:nth-child(2){
            /* 单体侧轴对齐 */
            align-self: center;
        }
        .box div{
            /* float: left;
            margin: 50px; */

            
            width: 200px;
            height: 100px;
            background-color: pink;
        }
    </style>
</head>
<body>
    <div class="box">
        <div>1</div>
        <div>2</div>
        <div>3</div>
    </div>
</body>
</html>